Indirect heater for magnetron



March 1, 1960 Filed Jun. 11, 1959 E. C. OKRESS INDIRECT HEATER FOR MAGNETRON 2 Sheets-Sheet 1 INVENTOR ATTORNEY March 1, 1960 E. c. OKRESS 2,927,241

INDIRECT HEATER FOR MAGNETRON I Filed June 11, 1959 2 Sheets-Sheet 2 Fig. 2

INVENTOR ERNEST O. QKRESS ATTORNEY United States Patent INDIRECT HEATER FOR MAGNETRON Ernest C. Okress, Elmira, N.Y., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application June 11, 1959, Serial No. 819,794

7 4 Claims. (Cl. 313-337) This invention relates to resonant-cavity type magnetrons and more particularly to the construction of a cathode assembly for the magnetron.

A resonant-cavity type magnetron is a completely selfcontained transmitter in which a single vacuum envelope houses the resonant tank circuits, the cathode and anode of the generator, and the coupling for delivering highfrequency power. In accordance with the invention, the cathode assembly is provided with a heating element for heating the cathode structure and bursts of high voltage applied between the cathode and anode pull electrons from the cathode.

Essential to the operation of a resonant-cavity type magnetron tube is the constant axial magnetic field supplied by an external magnet uniformly over the entire anode-cathode region. Each resonant anode cavity behaves much like a simple capacitance-inductance resonant circuit, setting up an R-F magnetic field between cavities.

In the resonant-cavity type magnetron, the emission of electrons is furnished by a cathode which must be initially energized by heating. This may be done by direct heating such as, for example, a cathode of the cermet type or indirect heating by the use of a filament. In the cermettype cathode, which is a ceramic-metal mixture, the cathode structure becomes electrolyzed and causes cracking and destruction of the cathode structure and also in prior indirectly heated cathodes, the ceramic or insulating material used in supporting the cathode or heater became damaged or destroyed.

Accordingly, it is a broad object of the invention to provide a magnetron cathode assembly having its elements properly insulated and with a minimum of insulating material.

Another object of the invention is to provide an indirectly heated cathode assembly for a resonant-cavity type magnetron which may be used at elevated temperatures over extended periods of operation.

A further object of the invention is to support a heating filament element for a cathode element in a manner to prevent physical contact between the elements during use.

Other objects and features of the invention will become apparent to those skilled in the art from an understanding of the following detailed description of one embodiment of the invention as illustrated in the accompanying drawings, wherein:

Fig. 1 is a diagrammatic view showing the several component parts which comprise a magnetron assembly.

Fig. 2 is a sectional view through the cathode of Fig, 1 to show details of the invention.

Figs. 3 and 4 are sectional views taken on the lines 3-3 and 44 respectively of Fig. 2.

Referring to Fig. 1, the magnetron assembly is indicated at and is made up of a getter section indicated generally at 12, an anode and cathode section indicated generally at 14, a housing for the cathode leads and other structure indicated at 16 and a waveguide and associated structure indicated at 18. In Fig. 1 the cathode of the 2,927,241 Patented Mar. 1, 1960 'ice present invention is schematically shown in the dashed area and indicated at 20 to show its position relative to the other elements of the magnetron assembly.

As shown in Fig. 2, the cathode 20 is constructed of a cylinder or sleeve 22 which is formed of any suitable refractory material such as molybdenum and has a coating 24 on its outer surface formed, for example, of an electron-emissive thoria compound. Mounted exteriorly of the cathode ends are end closures 26 and 28 which are preferably formed of molybdenum and each is provided with a central aperture to receive other structure. The closures 26 and 28 are generally similar and, as indicated, each is in the form of a flat disk and has an annular flange 27 which terminates in an inwardly extending edge 30. The edge 30 of each closure as shown in Fig. 2 provides a tight or friction fit with the cylinder or sleeve 22 and forms with the cylinder 22 an enclosed compartment. A

A filament or heating element 32, which is preferably formed of a single strand of non-inductive tungsten wire, is disposed within the cylinder or cathode sleeve 22 and forms a double helical or reverse coil as shown. The

heating element 32 is supported within the cylinder 22 in a manner to prevent its physical contact with the walls of the cylinder and terminates as shown in the lower portion of Fig. 2 in spaced legs 34 and 36 and is bent at its other end to provide the reverse or double helix. As shown in Figs. 2 and 3, the legs 34 and 36 are respectively attached to plates 38 and 40, the plate 38 being spaced from the closure 28 while the plate 40 is in the form of a channel iron and abuts the inner face of the closure 28. As shown in Fig. 4, the reverse helix is formed by means of a loop formed in the filament at the end opposite legs 34 and 36 providing an eye 42 for a purpose which will be mentioned later.

A tubular conductor lead 44 extends through the central aperture in closure 28 and is in contact with the plate 40 which is fixed to the heating filament leg 36 and a rod conductor 46 is disposed axially of the tubular conductor 44 and is fixed to plate 38 which in turn receives the other leg 34 of the heating filament. The tubular conductor lead 44, in addition to supplying power to the heating filament 32, provides power for cathode sleeve 22. The tube and rod are-preferably formed of molybdenum and will be maintained out of physical contact with each other by some suitable arrangement in order to prevent short circuiting and current may be supplied to the heating filament 32 by lines 48 and 50, shown in the magnetron assembly of Fig. 1, which, although not shown, will be suitably connected to the tube 44 and rod 46.

The heating filament 32 is supported at its other loop end in a manner to permit contraction and expansion of the filament and thus prevent damage thereto and also to prevent short circuiting of the heating filament and associated structure with other structure of the cathode. For this purpose a bonnet is mounted on the closure 26 about its central aperture providing therewith a housing which receives a ceramic sleeve 62 and which is held in place by a washer or apertured plate 65 attached to the inner face of closure 26. A guide support 66 has one end received by the sleeve 62 and spaced from the plate 65 to provide an expansion chamber 68 with the free end of bonnet 60. At its lower end the guide support 66 is provided with a heat shield 69 and a pin 70. The guide pin 70 extends into loop or eye 42 formed by the helix and functions to maintain the heating filament 32 rigid while the heat shield reduces the heat effect on the ceramic sleeve 62 and associated structure.

From the above detailed description it will be apparent that the only insulating or destructible material used is the ceramic sleeve 62, all other material or parts being con- (of contact with the cylindrical housingwall.

, 2. A cathode assembly of the indirectlyheated type ducting material. The other parts are preferably constructed of molybdenum in order to withstand high temperatures which may reach upwardly of 1450 C, It will also be apparent'that theheati-ng element;32 will have sufficient rigidityrto-prevent interference with the cathode cylinder or sleeve 22 and yetwill have suflicient flexibility to :permit its axial movement and allow for expansion I andcontraction. Theclosures-Zfiand28 will function in the dissipationof heat from-the sleeve or cylinder22.

Although only a single embodiment of the present invention has been illustrated and described,-it;will be apparent to those skilled in the art that'various-changes and modifications may be made therein without departing the spirit of the inventionor from'the scope of the appended claims. V i

What'i sclaimedisr i I 1 A cathode assembly of" the indirectly'heated type for use in 1a resonant-cavity magnetron comprisinga cylindrical housingof refractory material, a pair cfcentrally ,apertured metallic closures, one -of-tsaid closures being secured to one end of the housing, and the otherclosure being secured to theother end of the housing, a heating filament withinsaid housing between said closures, said spaced :legs 'adjacent'one closure and a loopnportion adfilament comprising a reverse helix-providing a pair of spaced legs adjacent oneclosure-and-a loop-portiou-adiacent the other closure, "21 tubular'conductor having an inner end extending into the .apertureofone closure and a being disposed in electrically conducting-relation with 7 one leg'of said heating filament, a rodconductor disposed axially of said tubular conductor and being disposed in electrically conducting relation withthe other leg of said heating filament, a bonnet secured to the othenclosure about the central aperture, -a non'conducting sleeve mounted withinsaid bonnet, a guide support having its outer'end disposed in sliding engagement with saidsleeve and' its inner end received by said'loop portion'of the filament whereby the heating filament is-maintainedaout for use in a resonant-cavity magnetron comprising a cylindricalhousing of refractory materialpa-pairof centrally.

apertured .closures ofconducting metal, one of -;-said closures being secured to one end of the-housing, and the other closurebeing secured to the other end of thehousing, a heating filament'within said housing between said closures, said filament comprising a reverse helix providjacent the other closure, a tubular conductor having an inner end extending into theapertureof one closure and being disposed in electrically conducting relation with one leg of said heatingfilament, a rod conductor disposed axially of said'tubular.conductorand being disposed in electrically conducting relation -with-;the other; legnofsaid heating filament, a bonnet secured to the other closure about the central aperture, a non-conducting sleeve mounted within" said 'ibonn'et, a guide support having. its

- outer end disposed .insliding engagementwithisaid sleeve and itsinner' endreceived by said loop portion. of the filament and a annular plate withinv the cylindricaluhousing securedto said. guide Support between its ends; providing a heat shield for saidfilament.

4. Acathode assembly of theindirectlytheatcd type for use in a resonant-cavity magnetron comprising a 'cylindrical housing of: refractory material, a pair of centrally apertured= metallic closures, one of saidclos'ures being secured to one end-of the housing, and the othericlosure being secured to the other-end of vthehousing,-;a heating filament within-said housing betweenrsaid closures, said filament comprising: a reverse helix providing. a; pair of spacedilegs adjacent one closure and a loop portion adjacent-;the other closure a tubular conductor-shaving an 1 inner end' extending into the aperture of one. closure and being disposedin electrically conducting relation with one leg of said heating filament, a rod conductortdisposed axially of saidtubulanconductor and beingdising a pair of spaced legs adjacent oneclosure and a loop ,portionadjacent the other closure, "a tubular conductor having an inner end extending intothe aperture'of-one closure, a -first supporting plate between said tubular conductor and one leg of said heatingfilament, a rod conductor disposed axially of said tubular conductor, a second supporting plate between said rod conductor and the other leg of said heating filament, a bonnet secured to the other closure about itscentral aperture, anon-conducting sleeve mounted within said bonnet, a'guide support having its outer end disposed in'sliding engagement posed in Y electrically r conducting relation with the other leg of said heating filament, a bonnet secured to the other closure about the central aperture, a non-conducting sleeve mountedwithin said bonnet, aguide support having its outer end disposed in slidinggengagement with vsaid sleeve and 'itsinner end-received by said loopiportion of the filament and said closures. comprisingannularzdisks having flanged outer extensions thereoniwhichiare turned inwardly to frictionally engage the wall of the ;cylindrical housing. a

References Cited in the .file .of this patent UNITED: STATES PATENTS 2,815,465 Shelton .L'Dec, 3, I957 

